Conventional single-phase rectifier power electronic circuits suffer from high total harmonic distortion (THD) and poor power factor. A number of regulations have been enacted recently to control the harmonic content of line current drawn by the electronic equipment. As a result, researchers have been actively seeking development of power supplies which can comply with those regulations. In recent years, many circuits and control methods were reported, in which high-frequency switching techniques were used to shape the input current waveform becomes dominate in power factor correction (PFC). See for example: A. Prasada. P. D. Ziogas, and S. Manias, "A Novel Passing Waveshaping Method for Single-Phase Diode Rectifiers," PESC'89, pp. 99-105; I. Barbi and S. A. Oliveira da Silva, "Sinusoidal Line Current Rectification at Unity Power Factor with Boost Quasi-resonant Converters," In Proceedings of IEEE-APE'90, pp. 553-562; R. Erickson, M. Madigan, and S. Singer, "Design of a Simple High-Power-Factor Rectifier Based on the Flyback Converter," In Proceedings of IEEE-APEC'90, pp. 792-801; C. Cansein and I. Barbi, "A Unity of Power Factor Multiple Isolated Outputs Switching Mode Power Supply Using a Single Switch," APEC'91, pp. 430-436; I. Takahashi, R. Y. Igarashi, "A Switching Power Supply of 99% Power Factor By the Dither Rectifier," INTELEC 1991, pp. 714-719; M. J. Schutter, R. L. Steigerwald, M. H. Kheraluwala, "Characteristics of Load Resonant Converters Operated in a High Power Factor Mode," IEEE APEC 1991, pp. 5-16; M. Madigan, R. Erickson, E. Ismail, "Integrated High Quality Rectifier-Regulators," IEEE PESC 1992, pp.1-9; R. Redl, L. Balogh and N. O. Sokal, "A New family of single-stage isolated power-factor correctors with fast regulation of the output voltage," IEEE PESC'94 Record, pp. 1137-1144; P. Kornetzky, H. Wei and I. Barteseh, "A Novel One-Stage Power Factor Correction Converter," IEEE APEC'97 Proc., pp. 251-258; Y. S. Lee, K. W. Sui and B. T. Lin, "Novel Single-Stage Isolated Power-Factor-Corrected Power Supplies with Regenerative Clamping," IEEE APEC'97 Proc., pp. 259-265; L. Huber and M. M. Jovanovici, "Single-Stage, Single-Switch, Isolated Power Supply Technique with Input-Current Shaping and Fast Output-Voltage Regulation for Universal Input-Voltage-Range-Application," IEEE APEC'97 Proc., pp. 272-280.
The implementation of high frequency techniques can be classified into two categories, ie. two-stage scheme and one-stage scheme. In a two-stage scheme, an ac/dc converter with power factor correction is connected to the line, followed by a dc/dc converter. These two power stages can be controlled separately, and thus it makes both converters possible to be optimized. The drawbacks of this scheme are lower efficiency due to twice processing of the input power, larger control circuits, higher cost and low reliability.
One-stage scheme combines the PFC circuit and power conversion circuit in one stage. Due to its simplified power stage and control circuit, this scheme is potentially more efficient. The underline strategy of this scheme is to design the circuit in a certain way that allows its PFC circuit and power conversion circuit to share the same power switch. Several PFC circuits have been reported. See for example: C. Cansein and I. Barbi, "A Unity of Power Factor Multiple Isolated Outputs Switching Mode Power Supply Using a Single Switch," APEC'91, pp. 430-436; I. Takahashi, R. Y. Igarashi, "A Switching Power Supply of 99% Power Factor By the Dither Rectifier," INTELEC 1991, pp. 714-719; M. J. Schutter, R. L. Steigerwald, M. H. Kheraluwala, "Characteristics of Load Resonant Converters Operated in a High Power Factor Mode," IEEE APEC 1991, pp. 5-16; M. Madigan, R. Erickson, E. Ismail, "Integrated High Quality Rectifier-Regulators," IEEE PESC 1992, pp. 1-9; R. Redl, L. Balogh and N. O. Sokal, "A New family of single-stage isolated power-factor correctors with fast regulation of the output voltage," IEEE PESC'94 Record, pp. 1137-1144. These circuits are especially attractive in low cost, low power applications. However, some drawbacks still exist: a) owing to improperly sharing of the power switch, when the converter operates at high frequency, the unavoidable leakage inductance of their power transformers produce high voltage spike at the switching time, resulting in decreased efficiency; b) because the power switch performs both PFC and regulation purposes, their regulation capabilities are limited; and, c) at high current and low duty ratio operation, a high voltage presents on the bulk capacitor, resulting in a high rating in design and hence raising the cost. Recently, several single switch converter topologies have been presented to overcome the above drawbacks. See for example: P. Kometzky, H. Wei and I. Barteseh, "A Novel One-Stage Power Factor Correction Converter," IEEE APEC'97 Proc., pp. 251-258; Y. S. Lee, K. W. Sui and B. T. Lin, "Novel Single-Stage Isolated Power-Factor-Corrected Power Supplies with Regenerative Clamping," IEEE APEC'97 Proc., pp. 259-265; L. Huber and M. M. Jovanovici, "Single-Stage, Single-Switch, Isolated Power Supply Technique with Input-Current Shaping and Fast Output-Voltage Regulation for Universal Input-Voltage-Range-Application," IEEE APEC'97 Proc., pp. 272-280.
U.S. Patents have been proposed for AC/DC converters with power factor correction but fail to overcome the problems presented above. See for example, U.S. Pat. Nos. 5,224,025 to Divan et al.; 5,416,387 and 5,442,539 to Cuk et al.; 5,479,331 to Lenni; 5,510,974 to Gu et al.; 5,515,257 to Ishii; 5,559,688 to Pringle; 5,592,128 to Hwang; 5,594,629 to Steigerwald; 5,598,326 to Liu et al.; 5,600,546 to Ho et al.; and 5,619,404 to Zak.